Locking devices for relatively sliding parallel door panels have included conventional key operated locks as well as the use of a simple rigid bar placed between the sliding panel and the door jamb for supplemental security. The use of the bar to block the sliding movement of the sliding door panel, however, is limited, at least in its simple form, to instances where the sliding door is interiorly placed with respect to the fixed one of the two door panels. When the sliding door panel slides past the fixed door panel on the outside of the fixed panel, there is no way to place a simple blocking device which would be secure against easy removal.
Several attempts have been made to provide locking bars for different types of "patio doors" such as the ones shown in U.S. Pat. Nos. 3,608,940, 3,478,471, 3,328,920 and 3,821,884. Each of the devices disclosed in these patents is complex and requires extensive modification of the door and, in some cases such as in U.S. Pat. No. 3,608,940, the device requires the presence of a door frame with rather large dimensions and of suitable material to allow the attachment of the safety lock to the fixed door framing member. In instances where the glass door panel frame is constructed of an aluminum extrusion, for example, it would not be possible to attach a locking bar such as the ones disclosed in the aforementioned patents.